Water always has been precious in the American West. Early 19th-century mapmakers described most of the region as the “Great American Desert.” The scarcity of water in this brown and empty landscape has confined human occupation since the earliest Indian and Spanish settlements. Later settlers dammed the rivers and pierced the underground reservoirs, but the most they created were scattered oases of farms and towns across the high plains and dry uplands.

“The overriding influence that shapes the West is the desert,” University of Texas historian Walter Prescott Webb maintained. “That is its one unifying force.” Twentieth-century engineering has enlisted the Colorado River and other western rivers in the fight to subdue the desert. But the desert endures, and now threatens to cut short western economic progress.

Already agricultural irrigation is exhausting groundwater resources stored up over thousands of years. Many western cities are rapidly outgrowing sustainable water supplies. The once-mighty Colorado River, the lifeline for half of the western population, could be fully committed to human consumption by 1990 or earlier. Entire states and regions are skirmishing over limited river flows, with the economic prospects brought by assured water supplies at stake.